This invention relates to a heat exchanger and, more particularly, to a heat exchanger in which a heat exchange medium is passed through a shell in a heat exchange relationship to another fluid passing through a plurality of tubes supported within the shell.
Heat exchangers incorporating a plurality of tubes supported within a shell are well known. In these arrangements the tubes are usually supported at their ends by tube sheets and heads are provided at each end of the shell for circulating a heat exchange medium through the tubes in a heat exchange relationship to another fluid passing through the shell.
In view of the fact that water is often utilized as the fluid passing through the tubes and steam is often passed through the shell in heat exchange relation to the water, the tubes must normally be constructed of a material, such as stainless steel, that is resistant to the corrosive materials often contained in the water, while the shell structure may be constructed of a less expensive material, such as carbon steel. Therefore, since these two materials have different expansion coefficients, it can be appreciated that relative movement occurs between the tubes and the shell during operation of the heat exchanger at its relatively high operating temperature. Another consideration in this regard is that the tubes and the shell are subjected to different temperatures since the respective heat exchange fluids which influence them are at different temperatures. As a result, the systems for mounting the tube sheets and the heads relative to the shell must be designed to accommodate this relative movement.
Further problems exist in the design of heat exchangers of the above type when relatively high hydrostatic pressure loading occurs in the heads, the tubes and on the tube sheets as a result of higher operating pressures used in certain heat exchangers. In particular, an excessive hydrostatic load can cause failure of the systems for mounting one or both of the heads to the shell, or excessive tensile loading on the tubes, resulting in slippage of the ends of the tubes from the tube sheet, or damage to shell expansion joint, or excessive bending forces applied to tube sheet.
It is, therefore, an object of the present invention to provide a heat exchanger of the above type which accomodates relative movement between the tubes and the shell while maintaining a sealed connection between the heads or head assemblies and the shell.
It is a further object of the present invention to provide a heat exchanger of the above type in which the tubes are preloaded in compression so that they may withstand greater tensile loads occurring in operation than would normally be possible.
It is a still further object of the present invention to provide a heat exchanger of the above type in which relative movement between the tube sheet and the shell in excess of a predetermined amount is prevented.